Zeolites, both natural and synthetic, have been used in a variety of catalytic and adsorptive operations. Most zeolitic materials are porous ordered aluminosilicates having a definite (although often undetermined) crystal structure. The structure may have a number of small cavities interconnected by a number of still smaller channels. Those cavities and channels are uniform in size within a certain zeolitic material. The above mentioned catalytic and adsorptive processes make use of these cavities and channels since by proper choice of zeolite, the zeolite channels will reject some molecules because of their size and accept others.
These zeolites typically are describable as a rigid three-dimensional framework of silica and alumina wherein the silica and alumina tetrahedra are linked through common oxygens. Some zeolites, however, have atoms such as gallium or germanium in a portion of the framework positions. The charge balance of the zeolite may be satisfied by inclusion of a proton, metal, or ammonium cation. The catalytic and adsorption properties of the zeolite may be varied by changing the ions within the zeolite. Conventional ion exchange techniques may be used to change those cations.
There are a large number of both natural and synthetic zeolite structures. The wide breadth of such numbers may be appreciated by considering the work Atlas of Zeolite Structures by W. M. Meier and D. H. Olson, published by the International Zeolite Association.
The present invention, ECR-10, is a cesium-containing gallo-aluminosilicate or gallo-silicate having the following general chemical formula: EQU (Na, Cs).sub.2 O:(Al,Ga).sub.2 O.sub.3 :2 to 4 SiO.sub.2 :O to
Other gallosilicates are known. For instance, U.S. Pat. No. 3,431,219 to Argauer, issued Mar. 4, 1969, discloses a synthetic sodium gallo-silicate having a composition, in terms of oxide mole ratios: EQU 0.9.+-.0.2Na.sub.2 O:0.1 to 1 Ga.sub.2 O.sub.3 :3 to 12 Al.sub.2 O.sub.3 :3 to 6 SiO.sub.2 :3 to 12 H.sub.2 O
The x-ray diffraction pattern shows the structure that of zeolite Type X, a faujasite. No suggestion is made of cesium substitution. Selbin and Mason (J. Inorg. and Nuclear Chem., 20, p. 222 (1961)) had earlier reported the synthesis of a similar X type Gallium silicate at Si/Ga=2.8, and a Gallium sodalite at Si/Ga of unity.
An extensive review of similar materials (X and Y) compared the Si/Ga distributions with the Si/Al distributions (Vaughan et al, Amer. Chem. Soc. Symp. Ser. 218. p. 231 (1983)). A review of several Gallium substituted zeolites by Newsam and Vaughan (Proc. 7th Intl. Zeolite Conf., Elsever Press, p. 457 (1986)) showed that the substitution of Ga for Al does not necessarily increase the unit cell value, but may not change the cell parameters, and in the case of sodalite, reduce it. Barrer ("Hydrothermal Chemistry of Zeolites", Academic Press, p. 282 (1982)) has reviewed the earlier Ga substitution work up to the early 1980',s, which usually involves Ga substitution for Al in the conventional Si/Al range of the subject material (zeolite or non-zeolite). The unusual characteristic of ECR-10, in contrast to this previous work, is that Ga does not substitute into the RHO framework in the normal RHO compositional range, but in an entirely different range in which RHO does not occur in the Si/Al form. More extensive synthesis work in the gallo silicate system further extends these observations to the extreme case where gallum does not substitute at all for aluminum in some zeolites (e.g., zeolite A) (Vaughan, unpublished).
U.S. Pat. No. 4,208,305 to Kouwenhoven et al, issued June 17, I980, teaches a complex silicate containing iron/aluminum/gallium/germanium in the framework. The zeolitic material has a pore size greater than about 7 .ANG.; a size which is significantly larger than the disclosed
Most previous work on Cs containing systems at low silica ratios show that F (U.S. Pat. No. 2,996,358) and pollucite are the dominant structural forms. Previous syntheses in the TMA--Cs--Li system, however, show that several structural types are possible (Barrer and Sieber, J. Chem. Soc. Dalton, p. 1020 (1977)), and the ERC-10/RHO composition was not found.
U.S. Pat. No. 4,309,313 to Barrett and Vaughan, issued January 5, 1982, discloses a cesium-containing zeolite, denominated CSZ-1, having the formula:
0.05 to 0.55(Cs,Th).sub.2 0:0.45 to 0.95 Na.sub.2 O:Al.sub.2 O.sub.3 :3 to 7 SiO.sub.2 :0 to 10 H.sub.2 O
and shown to have a modified faujasite structure (Treacy et al, J. Chem. Comm., 1986, p. 1211).
U.S. Pat. No. 4,333,859 to Vaughan et al, issued June 8, 1982, discloses a high silica faujasite structure, CSZ-3, having the composition: EQU 0.02 to 0.20 Cs.sub.2 O:0.80 to 0.95 Na.sub.2 O:Al.sub.2 O.sub.3 :5 to 7 SiO.sub.2 :2 to 10 H.sub.2 O
U.S. Pat. No. 4,397,825 to Whittam, issued Aug. 9, 1983, discloses two zeolitic materials, Nu-6(1) and Nu-6(2), each having the composition: EQU 0.5 to 1.5 R.sub.2 O:Y.sub.2 O.sub.3 :at least 10 XO.sub.z :0 to 2000 H.sub.2 O
where R is a monovalent cation, x is silicon and/or germanium and Y is one or more of aluminum, iron, chromium, vanadium, molybdenum, antimony, arsenic, manganese, gallium or boron, and show characteristics typical of layer type metallo-silicates.
Recent structural work has indicated that ECR-10 is a low silica analogue of the RHO structure, synthesized in a high silica aluminous form by Robson (U.S. Pat. No. 3,904,738). (One notes, however, that this conclusion is based on the interpretation of powder x-ray diffraction data, and must therefore be viewed as tentative, though convenient at this time. Spectroscopic analyses, such as infra-red analysis, does not confirm this identity.)
This gallium low silica ECR-10 form of RHO is unusual in that whereas most low silica forms of zeolites have larger unit cells than the corresponding higher silica forms, ECR-10 has a smaller unit cell than RHO itself. Similarly, because the Ga--O bond distance is larger than the Al--O bond distance, the Ga forms of a given structure also usually have a larger unit cell than the analogous Al forms-again contrary to the observation of ECR-10. The ECR-10 is therefore quite anomalous, indicating a compacted or more constrained environment than the actual (silica-alumina) RHO structure. Work by Barrer et al (Proc. 5th Intl. Zeolite Conf., Heyden Press, p. 20 (1980)) shows that the optimum synthesis is carried out at an Si/Al=11.
The compositions of the Al RHO and Ga ECR-10 may be compared as follows:
______________________________________ RHO: 0-1 Na.sub.2 O:0-1 Cs.sub.2 O:Al.sub.2 O.sub.3 :5-12 SiO.sub.2 ECR-10: 0-0.6 Na.sub.2 O:0.4-1 Cs.sub.2 O:x Al.sub.2 O.sub.3 :1-x Ga.sub.2 O.sub.3 :2-4 SiO.sub.2 ______________________________________
where x=O to 0.25
It is useful to note that not only does Ga not substitute significantly into RHO, but Al does not significantly substitute into ECR-10, further demonstrating the novelty of the substitutional and structural chemistry of these two materials.
Unlike RHO itself, Cs is much more difficult to remove from ECR-10. If Ga is attempted to substitute directly in the RHO preparation composition range the faujasite like zeolites CSZ-1 and CSZ-3 form, together with pollucite and F. If Al is substituted directly in the ECR-10 formulation to replace Ga, pure zeolite F results. The synthesis of ECR-10 is therefore unexpected and unpredictable in this composition range. Indeed, if the Ga-0 bond is too large to substitute at the higher level of Si, it would be even less likely to substitute at lower Si levels.